The present application generally relates to exhaust aftertreatment systems, and more particularly, but not exclusively, to selective catalytic reduction (“SCR”) systems.
Presently available SCR systems adsorb ammonia (NH3) on a catalyst and then react the NH3 with NOx to reduce the NOx emissions. The NH3 is typically stored as a less reactive composition, e.g. urea, and hydrolyzed into NH3 in the exhaust system as required to reduce the NOx emitted by the engine. At certain system operating conditions, the catalyst may produce secondary emissions of catalytic material. The possibility of emission of catalytic material has led to resistance of adoption of certain types of SCR catalysts, such as vanadium based SCR catalysts. In addition, SCR systems are known to create “ammonia slip” in which ammonia that does not adsorb slips through the SCR catalyst.
SCR systems also typically employ a diesel particulate filter upstream of the SCR catalyst. Available techniques for diesel particulate filter (“DPF”) diagnostics suffer from a number of disadvantages, drawbacks and inadequacies including an inability to adequately diagnose DPF loading and loss of filtration efficiency among others.
Therefore, a need remains for systems and methods for treating secondary emissions, including those comprising catalytic material and ammonia slip. A need also remains for improving diagnostic capabilities of diesel particulate filter conditions.